Of the various forms of heart disease, coronary artery disease and heart valve disease are two of the most widespread and debilitating. In coronary artery disease, growth of stenotic plaque in the coronary arteries causes the arterial lumen to narrow or close, restricting or cutting off blood flow to the heart muscle. Heart valve disease includes two major categories, namely stenosis, which is an obstruction to forward blood flow caused by a heart valve, and regurgitation, which is the retrograde leakage of blood through a heart valve.
The major surgical intervention for treatment of coronary artery disease is coronary artery bypass grafting, or CABG. In this procedure, while the patient is under general anesthesia, a median sternotomy or other gross thoracotomy is made, the patient is placed on cardiopulmonary bypass, and the heart is placed under cardioplegic arrest. An arterial or vein graft is then attached between a source of arterial blood, such as the aorta, and the diseased coronary artery downstream of the stenotic region, thereby providing a blood bypass around the stenotic region. While CABG generally has high efficacy, it is highly traumatic and has a significant complication rate associated with thoracotomy.
Similarly, when it is necessary to repair or replace a malfunctioning heart valve within a patient, heretofore the repair or replacement has been accomplished by a major open-heart surgical procedure, requiring a gross thoracotomy, general anesthesia and full cardiopulmonary by-pass with complete cessation of cardiopulmonary activity. Such surgery usually includes about three weeks of hospitalization and months of recuperation time for the patient. The average mortality rate with this type of procedure is about five to six percent, and the complication rate is substantially higher. Descriptions of open-heart procedures for replacing heart valves can be found in Gibbon's Surgery of the Chest, 5th Ed., David C. Sabiston, Jr., M.D., Frank D. Spencer, M.D., 1990, Vol. II, Ch. 52, pp. 1566-1596, and Textbook of Interventional Cardiology, Eric J. Topol, 1990, Chs. 43-44, pp 831-867.
Various non-surgical interventions have recently been developed to treat coronary artery disease. Non-surgical interventions include angioplasty, wherein a balloon catheter is advanced into the diseased coronary artery, and a balloon at the distal end of the catheter is inflated within the narrowed portion of the arterial lumen to crush the plaque and widen the arterial lumen. Another non-surgical intervention is atherectomy, wherein a catheter having a cutting blade at its distal end is advanced into the diseased portion of the coronary artery and the plaque is cut from the arterial wall and removed in the catheter. These interventions have enjoyed only limited success due to the high rate of recurrence of stenosis in the coronary artery following the procedure.
Some progress has also been made in developing endovascular procedures involving the heart valves. For example, for patients with severe stenotic valve disease, who are too compromised to tolerate open-heart surgery to replace the heart valve as described above, surgeons have attempted endovascular balloon aortic or mitral valvuloplasty. These procedures involve endovascularly advancing a balloon dilatation catheter into the patient's vasculature until the balloon of the catheter is positioned between the valve leaflets and then inflating the balloon to split the commissures in a diseased valve with commissural fusion and to crack calcific plaques in a calcified stenotic valve. However, this method may provide only partial and temporary relief for a patient with a stenotic valve. Rapid restenosis has been found to occur following the procedure in many cases.
An endovascular treatment regimen for regurgitant heart valves, which involves valve supplantation, has been disclosed in the patent literature, but apparently the procedure has not been clinically practiced. In this procedure, it is conceived that an elongated catheter is used to insert a mechanical valve into the lumen of the aorta via entry through a distal artery, for example, the brachial or femoral artery. One such mechanical valve is described in U.S. Pat. No. 4,056,854 (Boretos et al.) that is designed to be positioned against the artery wall during forward flow, as compared to the mid-center position of the valve described in U.S. Pat. No. 3,671,979 (Moulopoulos). The valve positioned against the arterial wall is intended to reduce the stagnation of blood flow and consequent thrombus and emboli formation compared to a valve at mid-center position. The mechanical valves previously described require an elongated mounting catheter extending out of the arterial entry point to maintain the position of the valve in the descending aorta. These valves would be expected to present several problems. The valves do not provide a permanent or internalized system. Furthermore, since both involve a mechanical valve, which predisposes the patient to thrombus formation and emboli, long term anticoagulant therapy is required. A serious complication of long term anticoagulant therapy is intracranial hemorrhage. Finally, the supplemental valve is placed downstream from both the normal valve position and the coronary ostia, so normal heart and coronary artery hemodynamics are not restored.
The descriptive terms upstream and downstream, when used herein in relation to the patient's vasculature, refer to directions closer to and further from the heart in the arterial system, and the opposite in the venous system. The terms proximal and distal, when used herein in relation to instruments used in the procedure, refer to directions closer to and farther away from the operator performing the procedure.
What have been needed and heretofore unavailable are methods and systems for satisfactorily performing various cardiac surgical procedures, particularly those suitable for coronary artery bypass grafting and for heart valve placement or removal and replacement, which do not require a thoracotomy. The present invention satisfies these and other needs.